THE KIDNEY
•T H E R O L E O F T H E K I D N E Y
•D I S S E C T I N G T H E K I D N E Y
LEARNING OUTCOMES
• 1. recall that the lungs, kidneys and skin are organs
of excretion (2.68)
• 2. describe the structure of the urinary system,
including the kidneys, ureters, bladder and urethra
(2.70)
REVIEW QUESTIONS
• The blood is to the circulatory system as ________ is
to the lungs.
• The _______ is to the circulatory system as lungs are
to the respiratory system
• Amino acids are to proteins as _______ are to
carbohydrates
ORGANS OF SECRETION: SKIN
•
•
•
•
•
Role of the skin:
Protection against damage
Preventing entry of disease
Sense organ
Controlling heat loss
ORGANS OF EXCRETION: LUNGS
• The lungs take in
oxygen from the air
and remove
Carbon Dioxide
(excretion)
THE FUNCTION OF THE KIDNEY
The kidneys are essentially blood filters. Blood is brought to the
kidneys to be filtered by the renal artery. After filtering, the
blood is taken away again by the renal vein.
The kidneys have four functions:
1. Maintaining the water balance in the body by a process
called OSMOREGULATION
2. Reabsorption of useful substances into the blood
3. Adjustment of the levels of salts and ions in the blood
4. Excretion of urea and other metabolic wastes
Write this in the front of your books
WATER BALANCE:
• State three ways in which the body gains water
and three ways in which the body loses water
• What is the difference between the amount of
water lost and the amount of water gained by the
body?
• Why is this important? What is maintained in the
body by keeping this balance?
KIDNEY LOCATION IN HUMAN
• Two kidneys – each about
the size of a fist, and lie
at waist level at the back
of the body.
• Humans have two
kidneys. They are beanshaped organs,
approximately 11.5 cm
long, situated in the
abdominal cavity, just
below the ribcage, one
on either side of the spine.
They are embedded in
fatty tissue for protection.
A CLOSER LOOK AT THE KIDNEY
This is a human kidney. You have 2,
but can survive with only 1.
DIAGRAM OF THE KIDNEY
•
•
•
•
A longitudinal section through a kidney shows three distinct
areas:
an outer region called the cortex
a middle region called the medulla, and
an inner region leading to the ureter, called the pelvis.
DISSECTING A KIDNEY: WHAT TO LOOK
FOR
BLOOD SUPPLY TO KIDNEY
• Renal artery supplies
blood to kidney.
• Renal vein takes blood
away from kidney.
• Ureter connects
kidney to bladder
• Urethra connects
bladder to outside of
body it is where urine
leaves the body.
EXCRETION OF UREA
1. Urea is a waste product from the breakdown of proteins.
2. If more protein is eaten than is needed the body will have an
excess of amino acids, which cannot be stored by the body.
3. The excess amino acids are broken down by the liver, with
urea as a by-product.
4. Urea is toxic, and must be excreted from the body, so it is
passed into the blood to be filtered out by the kidneys.
5. It is then passed to the bladder for storage as urine, before
leaving the body.
Write this in the front of your books
PRODUCTION OF URINE
vena cava
renal vein
aorta
renal artery
cortex
renal vein
renal artery
ureter
kidney
bladder
pelvis
medulla
sphincter muscle
urethra
pyramid
ureter
HOW THE KIDNEYS WORK
Blood enters the kidneys (renal artery)
Millions of nephrons (mini-filtering
systems) sieve the blood
Needed substances are reabsorbed and
the waste products are removed in the form
of urine
Clean blood returned to the blood (renal
vein)
Urine carried to the bladder by tubes called
ureters
When the bladder is full, urine passes out
of the body via the urethra
Structure of the
nephron
Ultra Filtration- all
small molecules and
lots of water
Blood high
in urea
Blood low in
urea
Selective
reabsorption- useful
substances back into
blood from tubules
(water sugar ions)
Excretion of
waste- excess
ions and water
plus all urea as
urine
Urine to
bladder
WATER BALANCE
• Our bodies control the amount of water in our blood
and tissues through the endocrine system (hormonal
system)
• Like thermo-regulation, water balance is a negative
feed back system that relies on the hypothalamus in
the brain.
• Anti Diuretic Hormone (ADH) is released in the blood
to control how much water the kidneys release in
urine.
IF BODY HAS TO LITTLE WATER
Sensor
Hypathalmus
detects low
blood water
concentration
Response
Pituatory
gland
produces
more ADH
Kidney reabsorbs
more
water into
blood
Result
Less volume
of urine
produced
(more
concentrated
IF BODY HAS TOO MUCH WATER
Hypathalmus
detects high
blood water
concentration
Pituatory
gland
produces
less ADH
Kidney reabsorbs less
water into
blood
higher
volume of
urine
produced
(less
concentrated
CONTROL OF WATER
Pituitary gland
produces less
ADH
Kidneys excrete
more water in
urine
+ water in
blood
hypothalamus
- water in
blood
Pituitary gland
produces more
ADH
Blood enters
brain
Kidneys excrete
less water in
urine
WATER BALANCE
•
1.
2.
Healthy kidneys filter the blood to:
Remove waste products (from metabolism of the
food we eat and body cells).
Remove excess fluid to balance fluid levels in the
body
AND FINALLY……
Homework;
1. Revise for module test
2. Visit
http://www.bbc.co.uk/schools/gcse
bitesize/biology/humansasorganisms
/6homeostasisrev5.shtml.
work your way through the section
on kidneys and try the higher tier test.